1. Field of the Invention
The present invention relates to electrical systems and, more particularly, to electrical systems for reducing power consumption by electrical appliances.
2. State of the Art
Recent events have given urgency to what has always been a good idea: energy conservation. Energy conservation can be implemented simply by turning off power from appliances that are not in use. While power control can be done manually, e.g., people can turn off appliances when they are done using them and turn off lights as they leave a room, automated power control plays an important role in energy conservation.
Timers can be used to control power delivery. For example, business lights can be turned on automatically at the start of a business day and turned off automatically at its close. Alternatively, timers can control the duration for which an appliance is active. For example, a timer might turn off a hot air hand dryer after a fixed time; anyone wanting more time can reset the hand dryer. Many appliances, such a printers, enter a low-power “sleep” mode after a set period of non-use.
Ambient-light sensors can be used to control certain appliances. For example, street lamps can be activated in low light conditions, and deactivated when morning brings sufficient light that the artificial illumination is not required.
Motion sensors, such as occupancy sensors, can be used to supply power only when people are present. Security lights often combine ambient-light detection and motion detection. During the day, the lights remain off regardless of motion in their vicinity; however, at night, motion triggers the lights on.
Vending machines, particularly those that are refrigerated, pose special problems when it comes to energy conservation. Typically, a vending machine owner-operator places a vending machine in operation on the premises of another, and visits as necessary to refill the vending machine. The owner of the premises typically pays for the electricity consumed by the vending machine, and thus may have the biggest interest in saving power; however, the premises owner may be limited to unplugging the vending machine to save power during time of low usage.
However, unplugging or switching off a refrigerated vending machine can have the undesirable consequence that the vending items may warm up. In extreme cases, this may cause items to spoil as some artificial sweeteners in diet drinks cannot survive continual thermal cycling. However, even where spoilage is not a problem, customers might have the unpleasant experience of, for example, a warm soda if they purchase soon after the vending machine is turned on. Also, the product container may be wet due to condensation on warmup. Also, unplugging or switching off a vending machine risks losing sales and customers.
U.S. Pat. No. 6,243,626, commonly assigned to the assignee of the present invention, herein incorporated by reference in its entirety, discloses an appliance (e.g., vending machine) with an external power-management control subsystem that automatically couples/decouples the appliance to/from an electric power source (e.g., wall outlet) in response to control signals provided by one or more sensors/timing circuits. For example, a current sensor, time-of-day circuitry, an occupancy motion sensor, and timer circuitry can be used as inputs to a controller, which is programmed to automatically decouple the appliance from the wall outlet as follows. When the current level sensed by the current sensor is below a low threshold level, the occupancy motion sensor does not sense occupancy, and the time-of-day circuitry indicates the time is “off-hours”, the timer is set to a predetermined probationary period (for example, ½ hour). During this probationary period, the inputs values are periodically evaluated to determine whether shutdown is appropriate. During such periodic evaluations, if shutdown is determined not to be appropriate, the probationary period is aborted. Yet, if during such evaluations, it is determined that shutdown is appropriate and the probationary period lapses, the controller automatically decouples the appliance from the wall outlet, thereby “shutting down” the appliance.
These same inputs (and other inputs) can be used by the controller to automatically couple the appliance to the wall outlet, thereby activating the appliance. For example, any one of the following conditions can trigger the controller to automatically couple the appliance to the wall outlet: lapse of a countdown period provided by the timing circuitry; the occupancy motion sensor senses occupancy; the time-of-day circuitry indicates the time is “in-business-hours”; a temperature sensor indicates the ambient temperature level has risen to a level that requires cooling/activation of the appliance.
Refrigerated vending machines utilize a compressor for cooling. It has been observed by the inventor hereof from extensive field measurements that the compressors in coin-operated beverage vending machines operate in a fairly consistent manner. In nearly all cases, the compressor will cycle from four to six times per hour. Exceptions do occur, such as when the machine is reloaded with hot product in summer. Typically, such events are transient and once the product is cooled down, the compressor operations resume to four to six cycles per hour.
However, it has been observed by the inventor hereof that the compressor operations in glass front, consumer accessible beverage coolers varies broadly. The trade names for such beverage coolers are reach-in coolers, slide coolers, or visi-coolers. More specifically, it has been observed by the inventor hereof that the compressor cycling for a representative array of commercially available reach-in coolers vary from a minimum cycle time of eight minutes to a maximum cycle time of eleven hours. This extreme range of compressor cycle times can be attributed to the following factors:                doors on some of these machines do not close properly, which causes leakage of cool air and extended compressor run time;        glass front doors, even if operating properly, are much less energy efficient than the steel, insulated interior doors used in coin-operated beverage machines; and        poor maintenance leads to clogged compressor coils and increased compressor run time.        
Poor maintenance occurs from the fact that service calls to reach-in coolers generally occur only when the cooling systems completely fail, which is rare. In contrast, coin-operated beverage vending machines are typically better maintained because such machines require service calls more often due to their complex coin, mechanical vending, and electronic subsystems.
In such reach-in coolers (and other compressor-based appliances that have broadly varying compressor cycles), automatic power management control is difficult. More specifically, when the appliance is decoupled from its power source, it is difficult to determine when to recouple the appliance to its power source. The time period between the decoupling and recoupling of the appliance to the power source is referred to herein as the “shutdown time period.” This shutdown time period should be maximized for maximum energy saving.
Thus, there remains a need in the art for automatic power-management control of a reach-in cooler (and other compressor-based appliances that have broadly varying compressor cycles) that provides enhanced power conservation.